U.S. patent number 6,397,655 [Application Number 09/541,813] was granted by the patent office on 2002-06-04 for auto-calibration of a solenoid operated valve.
This patent grant is currently assigned to Husco International, Inc.. Invention is credited to Dwight Stephenson.
United States Patent |
6,397,655 |
Stephenson |
June 4, 2002 |
Auto-calibration of a solenoid operated valve
Abstract
Operation of an electrically operated valve is calibrated by
applying a gradually increasing electric current to the valve.
While that is occurring pressure at either the inlet or outlet of
the valve is measured to detect when the valve opens. When the
valve opens the level of the electric current then being applied to
the valve is employed to determine an initial current level to use
subsequently whenever the valve is to be opened.
Inventors: |
Stephenson; Dwight (Delafield,
WI) |
Assignee: |
Husco International, Inc.
(Waukesha, WI)
|
Family
ID: |
24161169 |
Appl.
No.: |
09/541,813 |
Filed: |
April 3, 2000 |
Current U.S.
Class: |
73/1.72;
73/168 |
Current CPC
Class: |
F15B
13/0442 (20130101); F15B 19/002 (20130101) |
Current International
Class: |
F15B
13/044 (20060101); F15B 13/00 (20060101); F15B
19/00 (20060101); G01L 027/00 () |
Field of
Search: |
;73/168,1.72 |
References Cited
[Referenced By]
U.S. Patent Documents
|
|
|
4690003 |
September 1987 |
McNennamy et al. |
4759224 |
July 1988 |
Charbonneau et al. |
5878647 |
March 1999 |
Wilke et al. |
|
Primary Examiner: Raevis; Robert
Attorney, Agent or Firm: Haas; George E. Quarles & Brady
LLP
Claims
What is claimed is:
1. A method for calibrating control of a fluid valve having an
inlet, an outlet and an electrically operated actuator, wherein
when the fluid valve is to be opened a predefined initial level of
electric current is applied initially to the electrically operated
actuator, said method comprising:
applying pressurized fluid to the inlet of the fluid valve;
applying an electric current at varying levels to the electrically
operated actuator;
measuring pressure at one of the inlet and outlet to produce a
pressure measurement;
determining from the pressure measurement when the fluid valve
opens;
determining a difference between a level of the electric current
which was being applied when the fluid valve opened and the
predefined initial level; and
changing the predefined initial level, in response to the
difference.
2. The method as recited in claim 1 wherein measuring pressure
comprises measuring pressure at the outlet when the fluid valve
controls flow of fluid to an actuator.
3. The method as recited in claim 1 wherein measuring pressure
comprises measuring pressure at the inlet when the fluid valve
controls flow of fluid from an actuator.
4. The method as recited in claim 1 wherein applying an electric
current at varying levels comprises applying a predetermined
current level to the electrically operated actuator, and
occasionally increasing the electric current until a determination
is made that the fluid valve is open.
5. The method as recited in claim 1 wherein determining from the
pressure measurement when the fluid valve opens comprises
determining when a given rate of change in the pressure occurs.
6. The method as recited in claim 1 wherein changing the predefined
initial level comprises setting the predefined initial level to a
fixed amount less than the level of the electric current which was
being applied when the fluid valve opened.
7. A method for calibrating control of a fluid valve having an
inlet, an outlet and an electrically operated actuator, wherein
when the fluid valve is to be opened a predefined initial level of
electric current is applied initially to the electrically operated
actuator, said method comprising:
(a) applying pressurized fluid to the inlet of the fluid valve;
(b) applying a electric current at a predetermined level to the
electrically operated actuator;
(c) measuring pressure at one of the inlet and outlet to produce a
pressure measurement;
(d) determining from the pressure measurement whether the fluid
valve is open or closed;
(e) if the fluid valve is determined to be closed, increasing the
electric current;
(f) repeating steps (c) through (e) until the fluid valve is
determined to be open;
(g) upon determining that the fluid valve is open, determining a
difference between the electric current then being applied to the
electrically operated actuator and the predefined initial
level;
(h) determining whether the difference is greater than a predefined
amount; and
(i) when the difference is greater than the predefined amount,
changing the predefined initial level.
8. The method as recited in claim 7 wherein measuring pressure
comprises measuring pressure at the inlet when the fluid valve
controls flow of fluid to an actuator.
9. The method as recited in claim 7 wherein measuring pressure
comprises measuring pressure at the inlet when the fluid valve
controls flow of fluid from an actuator.
10. The method as recited in claim 7 wherein determining from the
pressure measurement whether the fluid valve is open or closed
comprises determining that the fluid valve is open when a given
rate of change in the pressure occurs.
11. The method as recited in claim 7 wherein changing the
predefined initial level comprises setting the predefined initial
level to a fixed amount less than the level of the electric current
which was being applied when the fluid valve opened.
Description
BACKGROUND OF THE INVENTION
The present invention relates to pilot operated proportional
hydraulic valves which are electrically controlled, and
particularly to calibrating the control of such valves.
The application of hydraulic fluid to an actuator, such as a
cylinder and piston arrangement, can be controlled by a set of
solenoid operated pilot valves. A pump supplies hydraulic fluid
under pressure to an electro-hydraulic valve (EHV) assembly, such
as the one described in U.S. Pat. No. 5,878,647. The EHV assembly
includes a fluid distribution block on which four solenoid valves
are mounted to control the flow of fluid to and from chambers of a
hydraulic cylinder connected to the fluid distribution block. A
first pair of the solenoid valves governs the fluid flow to and
from the piston chamber of the cylinder, and a second pair of the
solenoid valves controls the fluid flow to and from the rod
chamber. By sending pressurized fluid into one cylinder chamber and
draining fluid from the other chamber, the piston can be moved in
one of two directions. The rate of flow into a chamber of the
cylinder is varied by controlling the degree to which the
associated supply valve is opened, which results in the piston
moving at proportionally different speeds.
Solenoid operated pilot valves are well known for controlling the
flow of hydraulic fluid and employ an electromagnetic coil which
moves an armature in one direction to open a valve. The armature
acts on a pilot poppet that controls the flow of fluid through a
pilot passage in a main valve poppet. The amount that the valve
opens is directly related to the magnitude of electric current
applied to the electromagnetic coil, thereby enabling proportional
control of the hydraulic fluid flow. A spring acts on the armature
to close the valve when electric current is removed from the
solenoid coil. An example of a solenoid operated pilot valve of
this type is described in the aforementioned U.S. Patent.
Such proportional solenoid valves usually have a spring preload
force that acts on the pilot poppet. As a consequence a substantial
current level is required to produce an electromagnetic force that
overcomes the spring force and produces opening movement of the
pilot poppet. If the control circuit commences applying current to
the valve from zero when the operator first moves a manual control
device, that device must be moved a certain amount before
sufficient current is applied to the electromagnetic coil to open
the valve. This produces a dead band of wasted motion of the manual
control device.
To overcome this dead band problem, control circuits have been
designed to apply a predefined current level above zero upon
initial movement of the control device. In other words as shown in
FIG. 1, the current applied to the electromagnetic coil jumps from
zero to that predefined initial current level I.sub.INT when the
operator initially moves the control device from the off position.
The predefined initial current level is set to produce a force on
the armature of the solenoid that is slightly less than the spring
preload force. Thus the valve does not open immediately when the
control device is moved from the off position. As the control
device continues to be moved the coil current increases causing
pilot valve to open thereby producing a small flow through the
valve. Eventually the coil current increases to a level I.sub.O at
which the main valve poppet opens. This operation virtually
eliminates the dead band of wasted operator motion. The difference
between the initial current level I.sub.INT and the current level
I.sub.O at which the main valve poppet opens is referred to an the
"margin".
A problem in this operation arises due to relaxation of the spring
preload force with age which results in the valve opening at a
significantly lesser force produced by the electromagnetic coil,
thus decreasing the margin. Such relaxation can result from fatigue
of the valve spring, deformation of the pilot poppet-seat
interface, or deformation of the main poppet-seat interface. In
pressure compensated solenoid valves, changes in the compensation
mechanism with age also produces relaxation of the spring preload
force. When significant relaxation occurs, the valve may jump from
a closed position to a substantial flow position when the initial
current level is applied to the valve. This inhibits control at low
flow rates.
SUMMARY OF THE INVENTION
The present invention provides a method for calibrating control of
a fluid valve having an inlet, an outlet and an electrically
operated actuator. When the fluid valve is to be opened, a
predefined initial level of electric current is applied initially
to the electrically operated actuator. The calibration involves
applying pressurized fluid to the inlet of the electrically
operated valve and applying an electric current at varying levels
to the electrically operated actuator. The pressure at one of the
inlet and the outlet is measured, thereby producing a pressure
measurement which is employed to determine when the fluid valve
opens. For example, opening of the valve is indicated when the rate
of change of the measured pressure changes more than a given
amount.
A difference between the electric current level which was being
applied when the fluid valve opened and the predefined initial
level then is calculated. The predefined initial level is changed
in response to that difference. In the preferred embodiment of the
invention, the predefined initial level is set to a fixed amount
less than the level of the electric current which was being applied
when the fluid valve opened. This calibration ensures that the
initial level of current applied to open the valve will be a
desired amount less that the current level at with the valve begins
to open. Thus uniform operation of the valve occurs, even as the
valve ages.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing the relationship between electric current
applied to a proportional solenoid valve and fluid flow;
FIG. 2 is schematic diagram of a hydraulic system that incorporates
the present invention; and
FIG. 3 is a flowchart of a software routine that is executed by a
controller to recalibrate electrical operation of the proportional
solenoid valve.
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 2, electro-hydraulic valves are utilized in
a hydraulic system 10 to control bidirectional movement of an
actuator 11. The actuator 11 may comprise a piston 12 within a
cylinder 13 thereby defining a piston chamber 14 and a rod chamber
15 on opposite sides of the piston. Application of pressurized
fluid to one or the other of those chambers 14 or 15 produces
movement of the piston 12 within the cylinder. Such pressurized
fluid is produced by a variable displacement pump 16 having an
output connected to pump supply line 18.
The pump supply line 18 is coupled to the cylinder chambers 14 and
15 by a pair of inlet valves 20 and 22. Each inlet valve 20 and 22
is a solenoid operated, proportional valve and preferably has a
pilot poppet, such as the type described in U.S. Pat. No.
5,878,647, the description of which is incorporated herein by
reference. The output of the first inlet valve 20 is applied to the
piston chamber 14 of the actuator 11. Similarly, the output of the
second inlet valve 22 is applied to the rod chamber 15 of the
actuator 11.
The variable displacement pump 16 is controlled by a signal at a
control input 24. This signal is produced in response to the
greatest load pressure from the cylinder chambers 14 and 15. For
that purpose, each of the chambers 14 and 15 is connected by a
separate check valve 26 and 27, respectively, to a load sense line
28, which at any given point in time carries a pressure signal
corresponding to the greatest pressure in those cylinder chambers.
That pressure signal is applied to a load sense circuit 30 that
responds by producing the control signal at the control input 24 of
the variable displacement pump 16. Alternatively, the check valve
26 and 27 and the load sense line 28 can be replaced by an
electrical load sensing mechanism.
A first pressure sensor 31 is connected to the pump supply line 18
and provides a signal indicating the pressure in that line to a
controller 25. The supply line from the inlet valves 20 and 22 to
the cylinder chambers 14 and 15 also have separate pressure sensors
32 and 33, which send signals to the controller 25. Pressure
sensors 32 and 33 provide input signals that respectively indicate
the pressures in the piston and rod chambers 14 and 15.
The chambers 14 and 15 of actuator 11 are connected by third and
fourth outlet valves 34 and 36 to a fluid reservoir, or tank 38,
for the hydraulic system 10. Each outlet valve 34 and 36 is a
solenoid operated, proportional valve of the same type as the inlet
valves 20 and 22.
All the inlet and outlet valves are controlled by electrical
signals from the controller 25 that are produced in response to the
operator activating a manual control device, such as joystick 45.
Depending upon the amount to which the operator moves the joystick
45, the controller 25 varies the magnitude of current applied to
the respective valves which determines the degree to which the
valve opens and thus the rate of fluid flow through the valves. The
controller 25 is a microcomputer based device that executes a
software program which governs the operation of the hydraulic
system 10.
A fourth pressure sensor 40 provides an input signal to the
controller 25 which indicates the pressure in a line 42 leading
from the first and second outlet valves 34 and 36 to the fluid
reservoir 38.
Periodically, the controller 25 calibrates the inlet and outlet
valves 20, 22, 34 and 36 to ensure that the margin between the
initial coil current and the current level at which the each valve
opens remains at the desired value. Prior to initiating the
calibration procedure, the operator places the member of the
machine, which is controlled by the actuator 11, into a non-load
bearing position. On a lift truck for example, the mast would be
lowered completely in order to calibrate the hydraulic valves for
the mast actuator.
With the actuator 11 in the non-load bearing position, the operator
activates a calibration switch 44 which sends a signal to the
controller 25. In response to that calibration signal, the
controller commences executing a software routine which implements
the calibration procedure 50 depicted in FIG. 3. Calibration also
can be activated automatically upon equipment shutdown when the
actuators typically are placed into a non-load bearing
position.
At the first step 52 of the calibration procedure 50, the
controller 25 opens the outlet valves 34 and 36 for a predefined
interval of time. That interval has a sufficient duration so that
any fluid pressure trapped within the chambers 14 and 15 of the
actuator 11 will be released by draining the hydraulic fluid to the
system tank 38. The software execution then advances to step 54
where the controller 25 issues a command to the load sense circuit
30 to raise the output pressure of pump 16 to a predefined level.
Then the electric current I.sub.C that is applied by the controller
25 to the electromagnetic coil of the first input valve 20 is set
to the first current level at step 56. The first current level is
less than the initial current level I.sub.INT in the graph of FIG.
1.
Referring again to FIGS. 2 and 3, the input pressure to the
associated chamber 14 of the actuator 11 then is measured by the
controller 25 reading the output signal from the pressure sensor 32
at step 58. At step 60 if there was a previous pressure
measurement, the two measurements are utilized to calculate the
rate of rise in pressure in the cylinder chamber 14. Because the
pressure is measured at fixed time intervals, that rate of rise can
be determined merely by calculating the difference between the most
recent pressure measurement and the previous pressure measurement.
The controller 25 then determines at step 62, whether the rate of
pressure rise exceeds a given threshold amount which indicates that
the main poppet of the first inlet valve 20 has opened. If that
threshold has not been exceeded, indicating that the first inlet
valve 20 remains closed, the program execution branches to step 64,
where the coil current I.sub.C applied to the first inlet valve 20
is increased by a fixed amount. If the desired current margin
between levels I.sub.INT and I.sub.O in FIG. 1 is 0.1 amps, for
example, the coil current may be increased by 0.01 amps. That new
current level that is applied to the electromagnetic coil of the
first input valve 20 and steps 58-64 are repeated until the rate of
pressure rise exceeds a predefined threshold value X at step
62.
When this occurs, the existing margin is calculated by the
controller at step 66. Specifically, the margin is the coil current
level I.sub.O at which the valve opened minus the level of the
initial current I.sub.INT. Then a determination is made at step 68
whether the existing margin differs from the desired margin by more
than a given amount Y. This indicates that the actual margin has
decreased significantly below the desired margin value. If such a
decrease has occurred, the program execution advances to step 70
where the initial current level I.sub.INT is set equal to the
present current level I.sub.C, at which the valve opened, minus the
desired margin. This new value for the initial current level
I.sub.INT is stored in the memory of the controller 25, thereby
recalibrating the operation for this first input valve 20.
A determination then is made at step 72 whether there is an
additional inlet valve (e.g. 22) to calibrate. If so, that valve is
selected and the process returns to step 56 where the process
repeats for that other valve. When all of the valves have been
calibrated the procedure 50 terminates.
A similar procedure can be utilized to calibrate the outlet valves
34 and 36. In this case, the inlet valves 20 and 22 are both opened
and so as to apply pressure from the pump 18 through the chambers
14 and 15 of the actuator 11 to the inlets of both outlet valves 34
and 36. The inlet valves 20 and 22 are then closed to trap the
pressure in the cylinder chambers. Next, the controller 25 applies
current to the electromagnetic coil of the selected outlet valve
and gradually increases that current while monitoring the pressure
in the corresponding chamber 14 or 15 of the actuator 11. That
pressure is indicated by the pressure sensor 32 or 33 associated
with that cylinder chamber.
When the selected output valve 34 or 36 opens the associated
pressure drops significantly. When that occurs the current I.sub.C
that is being applied to the electromagnetic coil of the valve
corresponds to the current level I.sub.O at which the valve opens.
That current level I.sub.C along with the initial current I.sub.INT
for the outlet valve then are used as previously described to
determine whether the current margin should be reset.
* * * * *